 
 (defn intersection
   "Return a set that is the intersection of the input sets"
-  {:added "1.0"}
   ([s1] s1)
   ([s1 s2]
      (if (< (count s2) (count s1))


(defn rename
  "Returns a rel of the maps in xrel with the keys in kmap renamed to the vals in kmap"
  {:added "1.0"}
  [xrel kmap]
    (set (map #(rename-keys % kmap) xrel)))

(defn index
  "Returns a map of the distinct values of ks in the xrel mapped to a
  set of the maps in xrel with the corresponding values of ks."
  {:added "1.0"}
  [xrel ks]
    (reduce
     (fn [m x]

(difference #{:a :b :c} #{:c :d :e})
(intersection #{:a :b :c} #{:c :d :e})

(index ys [:b]))

